The microstructure of the CuGaSe2 (CGSe) thin films deposited by a novel chemical close-spaced vapour transport (CCSVT) technique on clean and Mo-coated soda lime glass (SLG) substrates has been investigated by transmission electron microscopy (TEM). The CGSe bulk and the interface between the CGSe and Mo films have been investigated. The as-grown CGSe films possess high bulk crystalline quality. At the CGSe/Mo interface, a MoSe2, interfacial layer (similar to 20-40 nm) has been observed and also an excess of Ga. Additionally, composition measurements and depth profiling of the elements were performed by elastic recoil detection analysis (ERDA). It has been found that the CGSe constituent elements are homogeneously distributed in the bulk, whereas the surface composition is influenced by the [Ga]/[Cu] ratio in the film. With the [Ga]/[Cu] ratio increase, the CGSe surface composition changes from Ga-and Cu-poor, and Se-rich to Cu-poor, and Ga- and Se-rich. Photoluminescence (PL) spectroscopy has been used as a complementary technique to study the defect profiles at the CGSe front and rear sides as a function of the [Ga]/[Cu] ratio. The PL data support the results of structural investigations, pointing out higher Ga concentration at the films rear side. (c) 2004 Elsevier B.V. All rights reserved.